Abstract

Seawater is a relatively complex mixture of dissolved salts that is dominated by six major ions: Na+, K+, Mg2+, Ca2+, Cl- and SO42 -. When seawater freezes in high latitude environments on Earth, the presence of these dissolved salts markedly affects the microstructure of the ice that forms, resulting in sea ice that is permeated by countless inclusions of concentrated seawater brine. The brine inclusions represent the site of all chemical and biological reactions in sea ice, and become increasingly saline with decreasing temperature. The paired effect of changing temperature and salinity results in dramatic changes to mineral solubility within the brine, which results in the precipitation of a whole suite of minerals within the sea ice microstructure. Each mineral displays a distinct behaviour and role within the sea ice system.

This talk tells the story of one of these sea ice minerals, mirabilite (Na2SO4·10H2O). Mirabilite has never been identified in sea ice in the field, but through a range of laboratory investigations it will firstly be shown that it is likely to be omnipresent in the sea ice environment below –6.4 °C. Secondly, the effects of mirabilite precipitation on the geochemical properties of the sea ice brine system will be evaluated. Lastly, the significance of these changes in relation to the measurement of salinity in the sea ice brine environment, which is a crucial physico-chemical property of the sea ice biome, will be outlined.